XEP-0096: SI File Transfer

Abstract:

This specification defines a profile of the XMPP stream initiation extension for transferring files between two entities. The protocol provides a modular framework that enables the exchange of information about the file to be transferred as well as the negotiation of parameters such as the transport to be used.

WARNING: This document has been Deprecated by the XMPP Standards Foundation. Implementation of the protocol described herein is not recommended. Developers desiring similar functionality are advised to implement the protocol that supersedes this one
(XEP-0234).

The traditional mechanism for transferring files in the Jabber community is the Out-of-Band Data (XEP-0066) [1] protocol. That protocol has several drawbacks:

It is not reliable.

It does not work when one of the parties is behind a firewall.

It provides limited metadata about files to be exchanged.

The current document defines a profile of Stream Initiation (XEP-0095) [2] that solves the problems with out-of-band data, thus providing a robust, reliable mechanism for file transfers over the Jabber network. Implementors are referred to XEP-0095 regarding the underlying concepts of stream initiation.

The file transfer profile is in the
"http://jabber.org/protocol/si/profile/file-transfer" namespace.
The profile is fairly simple: it consists of the root element
with the possibility of one child describing the optional ranged transfers.

The root element is <file> and has four attributes. The attributes
are used only during the offer stage of stream initiation:

The size and name attributes MUST be present in the
profile. The other attributes MAY be present.

There are two possible child elements of the root: <desc> and
<range>. Both are OPTIONAL.

<desc> is used to provide a sender-generated description of the file so
the receiver can better understand what is being sent. It MUST NOT be sent in
the result.

When <range> is sent in the offer, it should have no
attributes. This signifies that the
sender can do ranged transfers. When a Stream Initiation result is sent
with the <range> element, it uses these attributes:

offset - Specifies the position, in bytes, to start
transferring the file data from. This defaults to zero (0) if not
specified.

length - Specifies the number of bytes to retrieve starting
at offset. This defaults to the length of the file from offset to the
end.

Both attributes are OPTIONAL on the <range> element. Sending no
attributes is synonymous with not sending the <range>
element. When no <range> element is sent in the
Stream Initiation result, the Sender MUST send the complete file starting at
offset 0. More generally, data is sent over the stream byte for byte starting
at the offset position for the length specified.

In order to enable seamless file transfer and appropriate fall-back mechanisms, implementations of this profile MUST support both SOCKS5 Bytestreams (XEP-0065) [4] and In-Band Bytestreams (XEP-0047) [5], to be preferred in that order. The associated namespaces are to be included as option values for the "stream-method" variable as shown in the examples below.

As described below, the registered querytypes for file transfer actions are "sendfile" and "recvfile". Note well that "sendfile" means a second entity will send a file to the XMPP entity that controls the IRI/URI and that "recvfile" means a second entity will receive a file from the XMPP entity that controls the IRI/URI.

To enable a second entity to send a file, the IRI/URI is of the following form:

Example 9. Sending a File: IRI/URI

xmpp:romeo@montague.net/orchard?sendfile

The application SHOULD then present an interface enabling the user to provide information about the file to be sent (e.g., by "browsing" the file system of the user's computer in order to choose a file). As a result, the application SHOULD then send a Publishing Stream Initiation Requests (XEP-0137) [9] message to the XMPP address encapsulated in the IRI/URI:

Note well that the request to begin the stream is sent to the full JID (user@host/resource) of the XMPP entity identified by the XMPP IRI/URI. Therefore, the IRI/URI SHOULD include a full JID. If it does not, the receiver MUST discover a full JID via presence or service discovery. If the receiver cannot discover a full JID for the sender (e.g., in the last resort through sending a presence subscription request to the sender and receiving presence from the sender's resources), then it SHOULD abort the file transfer exchange.

Appendix C: Legal Notices

Copyright

Permissions

Permission is hereby granted, free of charge, to any person obtaining a copy of this specification (the "Specification"), to make use of the Specification without restriction, including without limitation the rights to implement the Specification in a software program, deploy the Specification in a network service, and copy, modify, merge, publish, translate, distribute, sublicense, or sell copies of the Specification, and to permit persons to whom the Specification is furnished to do so, subject to the condition that the foregoing copyright notice and this permission notice shall be included in all copies or substantial portions of the Specification. Unless separate permission is granted, modified works that are redistributed shall not contain misleading information regarding the authors, title, number, or publisher of the Specification, and shall not claim endorsement of the modified works by the authors, any organization or project to which the authors belong, or the XMPP Standards Foundation.

Disclaimer of Warranty

## NOTE WELL: This Specification is provided on an "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, express or implied, including, without limitation, any warranties or conditions of TITLE, NON-INFRINGEMENT, MERCHANTABILITY, or FITNESS FOR A PARTICULAR PURPOSE. ##

Limitation of Liability

In no event and under no legal theory, whether in tort (including negligence), contract, or otherwise, unless required by applicable law (such as deliberate and grossly negligent acts) or agreed to in writing, shall the XMPP Standards Foundation or any author of this Specification be liable for damages, including any direct, indirect, special, incidental, or consequential damages of any character arising from, out of, or in connection with the Specification or the implementation, deployment, or other use of the Specification (including but not limited to damages for loss of goodwill, work stoppage, computer failure or malfunction, or any and all other commercial damages or losses), even if the XMPP Standards Foundation or such author has been advised of the possibility of such damages.

IPR Conformance

This XMPP Extension Protocol has been contributed in full conformance with the XSF's Intellectual Property Rights Policy (a copy of which can be found at <https://xmpp.org/about/xsf/ipr-policy> or obtained by writing to XMPP Standards Foundation, P.O. Box 787, Parker, CO 80134 USA).

Appendix D: Relation to XMPP

The Extensible Messaging and Presence Protocol (XMPP) is defined in the XMPP Core (RFC 6120) and XMPP IM (RFC 6121) specifications contributed by the XMPP Standards Foundation to the Internet Standards Process, which is managed by the Internet Engineering Task Force in accordance with RFC 2026. Any protocol defined in this document has been developed outside the Internet Standards Process and is to be understood as an extension to XMPP rather than as an evolution, development, or modification of XMPP itself.

Appendix E: Discussion Venue

The primary venue for discussion of XMPP Extension Protocols is the <standards@xmpp.org> discussion list.

Appendix F: Requirements Conformance

The following requirements keywords as used in this document are to be interpreted as described in RFC 2119: "MUST", "SHALL", "REQUIRED"; "MUST NOT", "SHALL NOT"; "SHOULD", "RECOMMENDED"; "SHOULD NOT", "NOT RECOMMENDED"; "MAY", "OPTIONAL".

6. The Internet Assigned Numbers Authority (IANA) is the central coordinator for the assignment of unique parameter values for Internet protocols, such as port numbers and URI schemes. For further information, see <http://www.iana.org/>.

7. The XMPP Registrar maintains a list of reserved protocol namespaces as well as registries of parameters used in the context of XMPP extension protocols approved by the XMPP Standards Foundation. For further information, see <https://xmpp.org/registrar/>.